The present invention relates generally to piston dampers, and more particularly to a magnetorheological (MR) piston and damper.
Conventional piston dampers include MR dampers having a cylinder containing an MR fluid and having an MR piston which slideably engages the cylinder. The MR fluid passes through an orifice of the MR piston. Exposing the MR fluid in the orifice to a varying magnetic field, generated by providing a varying electric current to an electric coil of the MR piston, varies the damping effect of the MR fluid in the orifice providing variably-controlled damping of relative motion between the MR piston and the cylinder. The electric current is varied to accommodate varying operating conditions, as is known to those skilled in the art. A rod has a first end attached to the MR piston and a second end extending outside the cylinder. The cylinder and the rod are attached to separate structures to dampen relative motion of the two structures along the direction of piston travel.
A known design includes an MR piston having a substantially annular, magnetically energizable passageway and a magnetically non-energizable passageway positioned radially inward from the magnetically energizable passageway. The magnetically non-energizable passageway includes a check valve which is in either a valve closed position or a valve open position. The check valve blocks flow in one direction (usually when the rod moves more outward from the cylinder). The check valve allows flow in the other direction (usually when the rod moves more inward into the cylinder). The flow cross-sectional area of the magnetically non-energizable passageway is chosen for a particular damper application.
What is needed is an improved magnetorheological piston and an improved magnetorheological damper.
In a first expression of an embodiment of the invention, a magnetorheological piston includes a magnetorheological piston body having a substantially magnetically energizable passageway and having a substantially magnetically non-energizable passageway spaced apart from the magnetically energizable passageway. The substantially magnetically non-energizable passageway has a valveless passageway throat and has a flow cross-sectional area which has a minimum at the passageway throat and which is larger away from the passageway throat.
An alternate first expression is for a magnetorheological damper including a cylinder and the magnetorheological piston of the previously-described first expression. The magnetorheological piston is positioned within, and slideably engages, the cylinder.
In a second expression of an embodiment of the invention, a magnetorheological piston includes a magnetorheological piston body having a longitudinal axis, having a substantially magnetically energizable passageway substantially coaxially aligned with the longitudinal axis, and having a substantially magnetically non-energizable passageway spaced apart radially inward from the substantially magnetically energizable passageway. The substantially magnetically non-energizable passageway has a valveless passageway throat and has a flow cross-sectional area which has a minimum at the passageway throat and which is larger away from the passageway throat.
In a third expression of an embodiment of the invention, a magnetorheological piston includes a magnetorheological piston body having a longitudinal axis, having a core with an electrical coil, having a longitudinal end plate attached to the core, having a substantially magnetically energizable passageway substantially coaxially aligned with the longitudinal axis, and having a substantially magnetically non-energizable passageway spaced apart radially inward from the substantially magnetically energizable passageway. The substantially magnetically non-energizable passageway has a core portion and a longitudinal end plate portion. The substantially magnetically non-energizable passageway has a valveless passageway throat and has a flow cross-sectional area which has a minimum at the passageway throat and which is larger away from the passageway throat.
An alternate third expression is for a magnetorheological damper including a cylinder and the magnetorheological piston of the previously-described third expression. The magnetorheological piston is positioned within, and slideably engages, the cylinder.
Several benefits and advantages are derived from one or more of the expressions of a first embodiment of the invention. Having the substantially magnetically non-energizable passageway with a smaller flow cross-sectional area at a passageway throat and with a larger flow cross-sectional area away from the passageway throat limits the length of flow restriction to the length of a short passageway throat which prevents unwanted damper performance characteristics at low temperature (due to the high viscosity of low-temperature MR fluid), as can be appreciated by those skilled in the art. Locating the substantially magnetically non-energizable passageway (also known as the by-pass) radially inward from the substantially magnetically energizable passageway reduces the unwanted MR effect of valving the MR fluid flow in the substantially magnetically non-energizable passageway. Having the magnetorheological piston body include a core with an electrical coil and include a longitudinal end plate attached to the core, wherein the substantially magnetically non-energizable passageway includes a core portion and a longitudinal end plate portion, allows the passageway throat to be created by a monolithic portion of the longitudinal end plate, an orifice plug positioned inside this passageway in the longitudinal end plate, an orifice tube positioned inside this passageway in the core, or an orifice disc positioned inside this passageway longitudinally between the core and the longitudinal end plate. An MR piston having a tunable substantially magnetically non-energizable passageway is obtained by choosing an appropriate longitudinal end plate, orifice plug, orifice tube, or orifice disc having a desired orifice for a particular MR damper application.